Process for false-twisting a yarn

ABSTRACT

A process for false-twisting a yarn, which comprises passing a continuous filament yarn through the frictional engaging surface of two frictional rotors of the same diameter which face each other with the rotary shafts not being on the same axis and rotate in opposite directions to each other, wherein the yarn is fed to the frictional engaging surfaces at a speed of at least 500 meters per minute and imparted a tension defined by the following formula

United States Patent [1 1 Hino et a1. 0'

[111 3,772,873 [4 1 Nov. 20, 1973 PROCESS FOR FALSE-TWISTING A YARN [75]Inventors: Haziine Hino, Takatsuki; Nobuji Asaka, Suita; Masuo Tsuge,lbaragi; Sadao Tsuda, Takatsuki; Naoki Arai, lbaragi, all of Japan [73]Assignee: Teijin Limited, Osaka, Japan [22] Filed: Dec. 22, 1971 21Appl. No.: 210,816

[ 1 Foreign Application Priority llata Dec. 24, 1970 Japan ..45/l 18,372Dec. 25, 1970 Japan ..4S/l17,552

[52] US. Cl. 57/157 TS, 57/34 HS [51] Int. Cl D02g 1/02 [58] Field ofSearch 57/34 HS, 157 TS,

[56] References Cited UNITED STATES PATENTS 11/1964 Van Dijk et a1.57/77.4

l/1970 Asaka 57/157 TS 3/1968 Raschle 57/77.4

PHIrlEE EiEMirier-JOhn Petrakes Attorney-Leonard W. Sherman et a1.

[57] ABSTRACT A process for false-twisting a yarn, which comprisespassing a continuous filament yarn through the frictional engagingsurface of two frictional rotors of the same diameter which face eachother with the rotary shafts not being on the same axis and rotate inopposite directions to each other, wherein the yarn is fed to thefrictional engaging surfaces at a speed of at least 500 meters perminute and imparted a tension defined by the following formula 0.85 F6.35 X 10"V 0.100 wherein F is the tension of the yarn in grams perdenier, and V is the speed of feeding the yarn in meters per minute, ina twisting zone, and then the yarn is withdrawn from the frictionalengaging surfaces.

8 Claims, 8 Drawing Figures PMEMEnHum H375 3772.873

SHEET 2 BF 5 Fl o----@ 4 0 O iO A 0 B V 30- N E F2 A NUMBER OF FUZZES20- (PER MILLION METERS) x MORE THAN 100 I0 0 .MORE THAN l5 A MoRE THAN10 NOT MoRE THAN O [O YERN WITHDRAWING SPEED /min.)

PATENTEDHUVRO I975 3,772,873

SHEET 5 OF 5 Ill? PROCESS FOR FALSE-TWISTING A YARN This inventionrelates to a process for false-twisting a yarn stably at high speed bypassing a continous yarn such as multifilaments (to be referred tosimply as yarn) between the frictional engaging surfaces of twofrictional rotors of the same diameter opposing each other and rotatingin opposite directions to each other.

A method has previously been known in which a yarn is introduced betweencontact surfaces (this will often be referred to as engaging surfacehereinafter) of two frictional rotors of the same diameter rotating inopposite directions to each other (U.S. Pat. No. 3,156,084 and JapanesePatent Publication No. 1467/65).

It is generally thought that these frictional falsetwisting methods canbe operated at very high speed. But investigations have shown that theoperational stability of the method is poorer than has been previouslyimagined (this tendency is especially pronounced in the high speedprocessing, and false-twisting itself becomes impossible), and uniformcrimped yarns cannot be obtained. These false-twisting methods aredifferent from the frictional false-twisting method (for example,Japanese Patent Publication No. 2348/58) which has generally been usedin that a yarn is held between the frictional engaging surfaces of twofrictional rotors to thereby deliver and false-twist the yarn at thesame time. Therefore, in a high speed operation in which the processingspeed is at least 500 meters/min, it is extremely difficult to twist ayarn to adegree desired for crimped yarns and at the same time deliverthe yarn in a stable condition. These frictional methods, however, havethe characteristic that as compared with the above-mentioned frictionalfalsetwisting method, a yarn is not bent at the twisting portion. Thischaracteristic has an effect of reducing the formation of fuzzes in ahigh speed operation.

It is an object of this invention to provide a process for -tw stissatym at a ,sfisdqtmw tlrniOp meters per minute with reduced yarn breakageb'y passing a yarn between the frictional engaging surfaces of twofrictional rotors opposing each other and rotating in oppositedirections to each other.

The above object of the invention can be achieved by a process forfalse-twisting a yarn which comprises passing a yarn between thefrictional engaging surfaces of two frictional rotors of the samediameter, the rotors opposing each other and rotating in oppositedirections to each other, and the rotating axes of the two rotors beingnot on the same axis, wherein the yarn is fed to the frictional engagingsurfaces at a rate of at least 500 meters per minute, exerting a tensiondefined by the following expression wherein F, is the tension of theyarn. (gr/dc), and

V is the rate of feeding the yarn, on the yarn in a false-twising zone,and withdrawing the yarn from the frictional engaging surfaces.

The rate of feeding the yarn as mentioned herein is the speed of a yarnto be fed to frictional rotors which advances in a helical fashion. Inthe case of a nonstretchable yarn, this yarn speed is almost the same asthe speed of the yarn at feed rollers located upstream of the frictionalrotors. When the yarn is stretchable, the rate of feeding the yarn oryarn speed) can be measured at withdraw rollers where the yarn iswithdrawn under a tension (usually, about 0.1 g/d) required to removethe crimping of the yarn upon withdrawing from the frictional rotors.

In the conventional false-twisting processing at a relatively low speed,the number of rotations of the yarn per minute is at most 1,200,000 to1,500,000 r.p.m. (300 to 400 meters per minute) in the direct twistingmethod (for instance, Japanese Patent Publication No. 21494/65)utilizing frictional rotors or a method (for instance, US. Pat. No.3,156,084) in which a yarn is false-twisted by holding the yarn betweentwo frictional rotors rotating in opposing directions to each other, and600,000 rpm meters per minute) in the spindle method.

Furthermore, in the conventional false-twisting methods, it has beenconsidered best to process a yarn at the lowest possible tension (forexample, 0.1 gr/de to 0.15 gr/de) for the purpose of reducing yarnbreakage.

Investigations have been conducted the determine the factors whichrender the processing unstable, and led to the discovery that thegreatest factor is the generation of an extraordinary tension on theyarn at the twisting point of a false-twister due to balooning of theyarn, which tension renders the twisting action nonuniform, and causes astress concentrating point in the twisted yarn to an extent of yarnbreakage.

It has been found that contrary to the previous concept of processingtension, the yarn can be false-twisted stably with reduced yarn breakageby removing the balooning of the yarn utilizing a high stretching zoneof the yarn. Thus, it has been found that in order to remove suchbalooning, the yarn is processed at a yarn speed of at least 500 metersper minute while maintaining a tension F in the twisting zone at a valuedefined by the following empirical formula wherein Y F, is the tensionof the yarn (gr/dc), and

V is the speed of the yarn (meters/min).

If the tension F, in the twisting zone is higher than 0.85 gr/de,breakage of the yarn due tothe twisted structure of the yarn tends tooccur, although the balooning of the yarn does not take place. Also,fuzzes tend to occur, and there are extremely frequent yarn breakages.On the other hand, if F, is below 6.35 x 10V 0.167, the balooning of theyarn occurs occasionally at random, and when balooning occurs, the yarnrarely returns to the original state, which in turn may result in yarnbreakage.

Very superior false-twists can be imparted to the yarn when the twistingtension F, is defined as follows:

0.70 F, 6.35 X l0V- 0.100

The yarn breakage can be reduced as compared with the ordinaryfalse-twisting operations.

The invention will be further illustrated by reference to theaccompanying drawings in which:

FIG. 1 is a schematic view showing one example of the false-twistingstep according to the invention;

FIG. 2 is a graphic representation showing the relationship among thetwisting tension, withdrawing tension, and the number of fuzzes formed;

FIG. 3 is a view illustrating the components of the peripheral speed offrictional rotors used in the invention;

FIG. 4 is a perspective view showing one example of a liquid removingnozzle used in the invention;

FIG. 5 is a view showing the cooling method for frictional rotors in thepresent invention;

FIG. 6 is a sectional view of the twisting portion of a false-twistingdevice used in the invention;

FIG. 7 is a sectional view of the false-twisting device used in theinvention, in particular a fixed disc using radial ball bearings; and

FIG. 8 is a sectional view of the false-twisting device used in theinvention, in particular a freely-movable disc using a pneumaticbearing.

Referring to FIG. 1, yarn Y leaves a bobbin 1, and fed by a feed roller3 pressed by a press roller 2. It is heattreated by a heater 4, andafter passing guide 5, is falsetwisted by frictional rotors 6 and 7whose surfaces are covered with rubber. The yarn is then withdrawn by awithdraw roller 10 via a guide 9, and wound up on a package 12 by meansofa winder 11. The reference numeral 13 represents a wool-like cord, oneend of which is connected to a tank 14 containing liquid inert to theyarn, and from the other end of which the liquid is fed to the surfacesof the frictional rotors 6 and 7.

A nozzle for removal of the liquid is designated at 8, and is adapted toblow off the liquid contained in the yarn by air. The yarn isfalse-twisted while being held by the engaging surfaces of two opposingfrictional rotors of the same diameter rotating in opposite directionsto each other.

The twisting of the yarn is imparted between the frictional rotors 6 and7 and the feed roller 3 (to be termed a twisting zone). The tension ofthe yarn in the twisting zone is controlled mainly according to thespeed of the frictional rotors, and the interaxial distance between therotors. Delicate control can also be made by varying the contactpressure between the yarn and the heater 4, or the withdrawing speed ofthe withdraw roller 10.

The lower limit of the tension of the yarn in the twisting zone at whichtension the balooning of the yarn is removed, and the false-twistingoperation becomes stable was examined for various speeds using anapparatus of the type shown in FIG. 1 under the conditions shown inTable 1. In this experiment, the lower limit of tension at whichfalse-twisting could be performed for 30 hours without yarn breakagewa sdefined as the lower limit of tension for stable processing. The resultsobtained are shown in Table 2. It is seen from the results that at aprocessing speed of at least 500 meters per minute, a tension of atleast 6.35 X 10V 0.100 is required.

TABLE 1 Yarn: Polyethylene terephthalate, 75 denier/24 filamentsDiameter of the rotors: 90 mm Material of the frictional rotors:Polyurethane rubber with a hardness of 55 Interaxial distance of therotors: 48 mm Contact pressure of the rotors: 25 Kg Inclined angle ofthe rotors: 1

Inert liquid: water, 300 cc/min.

Length of the heater: 2m

Temperature of the heater:

300 meters/min. or less 220 C. 400 meters/min. 223 C. 500 meters/min.226 C. 600 meters/min. 230 C. 700 meters/min. 235 C.

800 meters/min. 240 C.

900 meters/min. 245 C.

1000 meters/min. 250 C.

TABLE 2 Lower limit of tension for stable processing (grams) Speed ofyarn (meters/min.)

The tension was measured between the heater 4 and the guide 5 of FIG. 1by means of an electron tension meter (product of Roschild Company,Switzerland). The figures in the parentheses show the detwisting tensionof the yarn.

It is seen form the results obtained that the lower limit of tensionrequired for false-twisting a yarn stably at a speed of 500 meters perminute or more is far higher than that required for false-twisting theyarn at lower speeds.

Furthermore, under the conditions shown in Table 1, the yarn tension forstable processing is between 35 and 64 g at a yarn speed of 1,000 metersper minute. In this case, the number of rotations of the yarn reaches asmuch as 3,200,000 rpm. As one example, when a twospindle machine wasoperated for a total of 2,520 hours at a processing speed of 1,000meters per minute using a tension of 45 2 g, six yarns were brokenduring this time, and this means that per yarn breakage, the processingwas continued for 420 hours. This is comparable to the conventionalfalse-twisting operation in which an average time needed for one yarnbreakage is 400 hours. In the conventional wooly processing, the tensionat the twisting zone is 7 i 1 g, and at such a tension, the processingspeed is at most 400 meters per minute. According to the process of theinvention, a processing speed unexpected from the conventional methodscan be attained. Thus, the processing can be made at extremely highspeeds.

In order to demonstrate further that according to the process of theinvention, stable twisting can be performed at a yarn speed of at least500 meters per minute, processability was examined using an apparatus ofthe type shown in FIG. 1 at varying tensions of the yarn in the twistingzone and at varying yarn speeds between 500 and 1,000 meters per minute.The conditions and the results obtained are shown in Table 3.

TABLE 3 Speed of yarn (meter/min.) Twisting tension (grams)Processability less than 8 (8) less than 12 (12) less than 17(19) lessthan 22 (22) less than 27 (27) less than 32 (32) The processability wasevaluated on a scale of three stages in which:

0 shows there was no yarn breakage for more than 30 hours;

A shows yarn breakage occurred in minutes to 30 hours; and

X shows yarn breakage occurred in less than 10 minutes or processingtotally failed.

It has been found that by employing the abovementioned tension, thebalooning the yarn can be eliminated, and a stable twisting can beperformed, but that the resulting crimped yarn has considerable fuzzes.

If the occurrence of fuzzes can be prevented, this high speed processingmethod is most desirable from the viewpoint of the quality of theproduct also. Therefore, this point was furthered in our research anddevelopment work. As a result, it was found that the twisting tensionshould be within the range of from 0.85 to (6.35 X l0"V- 0.100), and byrendering the withdraw tension lower than the tension within this rangea stable false-twisting operation and the prevention of fuzzes becomepossible.

The relation among the tension F, of yarn in the twisting zone, thetension F of yarn being withdrawn from the frictional rotors, and thenumber of fuzzes formed is shown in Table 4. The yarn used was apolyethylene terephthalate yarn (75 denier/24 filaments), and processedunder the conditions shown in Table 5. The apparatus used was al2-spindle machine, and the evaluation of the results was made withrespect to 300 kg of the yarn for each set of the conditions employed.

TABLE 4 F,(gr) F (gr) Speed of withdraw Number of fuzzes rollers(meters/min) (per million meters) 46 50 I040 837 46 44 I030 28 45 36I020 45 30 l0l5 5 45 25 mm 4 45 1008 4 45 I0 1000 3 TABLE 5 Frictionalrotors: 90 mm in diameter, made of polyurethane rubber having a hardnessof 55; interaxial distance 52 mm; contact pressure, 3.0 kg; counterangle of inclination 1 Inert liquid: 300 cc/min. of water Yarn feedrate: 1000 meters/min.

Length of the heater: 2 mm Temperature of the heater: 250 C.

The tension in the twisting zone was measured at a place between theheater and the frictional rotors, and the withdraw tension, between theguide 9 and the withdraw roller 10. The measurement of the tensions wasperformed using an electronic tension meter (product of RoschildCompany, Switzerland), The measurement of the number of fuzzes was madeusing a fuzz detector (product of Kasuga Electric Co., Ltd.), and thenumber of fuzzes per million meter of the yarn was counted whilemaximizing its sensitivity. It is seen from Table 4 that when thewithdraw tension F 2 is larger than the tension F, in the twisting zone,the occurrence of fuzzes becomes remarkable abruptly, and a crimped yarnof good quality cannot be obtained. On the other hand, if the tension Fis smaller than the tension F,, the occurrence of fuzzes is reduced, anda very good crimped yarn is obtained.

Table 6 shows the tension F, of yarn in the twisting zone, the withdrawtension F of yarn, and the number of fuzzes formed in the processing ofanylon 6 yarn denier/34 filaments) under the conditions shown in Table 7.It is seen from the table that for good results, the tension F of yarnin the twisting zone should be Frictional rotors diameter: 82 mmmaterial: nitrile rubber with a hardness of 52 interaxial direction: 33mm contact pressure: 0.7 kg

counter angle of inclination: 1 Inert liquid water 160 cc/min. Length ofthe heater The relation among the withdraw speed, the tension F, in thetwisting zone, the tension F in the withdrawing zone, and the extent ofoccurrence of fuzzes is shown in FIG. 2 with respect to a polyethyleneterephthalate yarn denier/24 filaments) processed at a yarn feed speedof 800 meters per minute under the conditions shown in Table 8. It isseen from FIG. 8 that the number of fuzzes changes greatly beyond theintersectiong point of the curves representing F, and F and that in thefalse-twisting process of the present invention, tension F, should belarger than the tension F Furthermore, in order to reduce the number offuzzes remarkably it is preferred that the withdraw tension F should benot more than percent of the twisting tension F,.

TABLE 8 Frictional rotors diameter: mm

material: polyurethane with a hardness of 55 interaxial distance: 48 mmcontact pressure: 2.5 kg

counter angle of inclination: 1

Inert liquid: water 300 cc/min. Yarn feed rate: 800 meters/min. Lengthof the heater: 2m

Temperature of the heater: 240C.

As shown above, in the false-twisting method using frictional rotors,different from the conventional spindle false-twisting method, theoccurrence of fuzzes can be reduced only when the withdraw tension F islower than the tension F of the twisting zone.

If the withdraw tension F is reduced to below 0.05 g/d, complicatedinterlacings are formed in the individual filaments which constitute thecrimped yarn, and when such yarn is woven into a fabric, the feel of thefabric is rough. Therefore, it is possible to obtain a woven fabricwhich has a different feel from that of a woven fabric made of ordinarycrimped yarns.

According to the present invention, therefore, the processing can beperformed at high speed of more than 500 meters per minuteand in astable condition,

and it is possible to obtain a crimped yarn of reduced fuzzes by such ahigh speed processing.

As previously mentioned, the tension of the twisting zone can bemaintained within the range required of the present invention by mainlycontrolling the rotation speed of the frictional rotors and theinteraxial distance between the two frictional rotors. It has beenfurther discovered that when the rotation speed of the frictional rotorsand the interaxial distance between the two frictional rotors satisfythe following relation with respect to the yarn, greater improvementscan be achieved in the stability of twisting operation and theoccurrence of fuzzes.

V/Yarn twisting speed (AT5) V/( V D e "777) 0.7-0.9

V/Yarn feeding speed R) V/(e1rr)= 1.05-1.40

wherein D is the diameter of the frictional rotors,

e is the interaxial distance between the frictional rotors (0,0'),

r is the speed of rotation of the frictional rotors, and

V is the speed of the yarn.

In other words, in order to perform the false-twisting process of theinvention effectively using frictional rotors made of rubber with ahardness of 40-70, the ratio of the yarn speed to the yarn twistingspeed should be 07-09, and the ratio of the yarn speed to the yarnfeeding speed should be 1.05-1.40. These requirements should be metsimultaneously.

If the ratio of the yarn speed to the yarn twisting speed is less than0.7, the twisted yarn assumes a state near the so-called double twist(also called kink twist) because of excessive twists. In particular,when the yarn speed is above 500 meters per minute, there is a tendencytoward yarn breakage in the twisting part, and stable processing cannotbe performed. If the ratio ofthe yarn speed to the yarn feeding speedexceeds 0.9, the usually desired number of twists are not imparted, andthe resulting yarn has a reduced value as crimped yarn.

On the other hand, if the ratio of the yarn twisting speed to the yarnfeeding speed is in the range of 0.7

to 0.9, but if the ratio of the yarn speed to the yarn feeding speed(AC) is smaller than 1.05, the tension F of the yarn in thefalse-twisting zone becomes higher beyond 0.85 gr/de, and there is afrequent breakage of yarn. If the ratio is larger than 1.40, the yarntension F 1 in the false-twisting zone becomes smaller than (6.35 X 10V-0.100). Thus, similarly to the case of excessive twist, yarn breakage atthe twisting portion becomes frequent, and stable processing cannot beperformed.

Japanese Patent Publication No. 16748 discloses that the ratio of theyarn speed to the surface speed of a twisting tube is optimum at 0.5 to0.9. Tracing experiments show however that this relation holds true withyarn of less than denier at a speed of up to 300 meters per minute. At ahigher speed above 300 meters per minute, especially more than 500meters per minute, the number of twists becomes a maximum at the aboveratio in the vicinity of 0.7. This number is less than percent of thatactually required, and it has also been confirmed that fuzzes occurfrequently, and good processing cannot be expected. Furthermore, with ayarn of denier, the speed ratio of 0.54 is an optimum value as shown inthe above-mentioned Japanese patent. On the other hand, in the presentinvention, the optimum value is obtained at a yarn speed- /yarn twistingspeed of around 0.80. This demonstrates that the false-twisting methodshown in the above Japanese patent differs in twisting action from thefrictional false-twisting method of the present invention.

In the practice of the process of the invention, the frictional surfacesof the frictional rotors 6 and 7 are preferably wetted with a liquidinert to the yarn which is fed from the tank 14 through the wool-likecord 13. This prevents the frictional rotors from stick slipping orburning during high speed processing operations, and stable high-speedtwisting can be performed. At this time, the yarn undergoes aconsiderable twisting moment on the engaging surfaces, and its physicalstructure tends to be changed greatly. Therefore, the liquid used forthe above-mentioned purpose should be inert to the yarn so that is doesnot extremely deteriorate the physical and chemical properties of theyarn during processing. Typical examples of the liquid include water,aqueous solutions containing textile finishing oils (for example,antistatic agents, or lubricants), or liquid textile finishing agents.

Such a liquid is applied to the engaging surfaces of the two frictionalrotors so that at least that part where the yarn comes into contact withthe rotors becomes wet. The application can be effected by a methodshown in FIG. 1. Also, it can be effected by a method wherein the liquidsurface of a liquid reservoir tank is pressed by pressurized air, andthe liquid or air containing the liquid is jetted out from a nozzle, ora method wherein a liquid level in a tank is utilized, or a method inwhich the liquid is sprayed by a sprayer.

The crimped yarn obtained from a false-twisting apparatus in such astate contains excessive amounts of the above liquid. When an excessiveamount of liquid is contained in the crimped yarn, the moistureplasticizes the yarn wound up on a bobbin, and with the passage of time,the amount of crimps is reduced. F urthermore, the liquid contained inthe yarn wound up on a bobbin evaporates gradually or diffuses intoother substances, and therefore, the liquid content of the yarndecreases. When the selling and buying of yarns are conducted on thebasis of weight, the liquid content fluctuates. In order to maintain theliquid content of the yarn at a constant or reduce it to nearly zero, anadditional moisture-controlling step or drying step becomes necessary,and the significance of reducing the cost by processing at high speedwill be lost.

Where a heater is provided at the rear of the false twisting apparatusto re-set the yarn (in the case of producing a heat-stabilized yarn),the efficiency is poor if a liquid is adhered to the yarn, and alsounevenness tends to occur. Furthermore, if the bobbin is a paper tube,it becomes wet and broken. Furthermore, molds are formed to deterioratethe quality of the yarn to a marked extent. Therefore, it is necessaryto remove the excessive liquid contained in the crimped yarn.

The crimped yarn tends to contain liquid more than ordinary filamentyarns, and the rate of yarn travel is high. it is therefore difficult toremove the liquid within a very short time, that is, over a shortdistance in the machine. The liquid could not be removed sufficiently bya method in which a rotary body having a diameter of not more than 20 mmis rotated at a speed of more than 5,000 rpm, and the liquid is thrownoff by a centrifugal force by winding the yarn around the rotary bodyseveral tens of times, a method wherein the yarn is passed through twosqueeze rolls to throw off the liquid, a method wherein the yarn isheat-treated on a heating roller, or a method wherein the liquid isremoved by passing the yarn through a heater.

it has now been found that by impinging a high speed air flow againstthe yarn between the false-twisting device and the take-up device, thedetrimental liquid adhered to the yarn can be removed in a very smallspace. Specifically, by passing the yarn through a nozzle 8 forcompressed air as shown in FIG. 1, a tubulent or swirling flow of highspeed air flow having a sonic speed or a speed near semisonic speed actson the yarn at right angles thereto or in parallel therewith, and theliquid adhering to the individual fibers is thrown away, thus wipingaway all liquid drops.

FIG. 4 shows one example of the pressurized air jetting nozzle used-inthe present invention. The reference numeral 1 represents a main body 1;2 and 3, yarn-passing slits; and 4, a pressurized air pipe. By thepressurized air fed from the pipe 4, the liquid adhering to the yarn Yis thrown away.

By using the above-described nozzle, compressed air is jetted out from ajet pipe in the nozzle, and collides directly with the yarn travellingalong the yarn path. If the pressure of the compressed air is low, theeffect of blowing away the liquid is poor, and if the pressure is toohigh, the liquid is violently blown off, but the efficiency becomes low.Furthermore, the liquid removing action differs somewhat according tothe diameter of the jet pipe or the angle of the jet pipe to the axis ofyarn.

As the pressure of compressed air suitable for the object of the presentinvention, pressures of at least 0.5 Kg/cm gauge can be used. if thepressure is below 0.5 Kg/cm gauge, the liquid contained in the interiorof the yarn'cannot be removed. Most desirably, a compressed air jet pipewith a diameter of at least 1.0 mm (area of at least 0.8 mm) is used forcompressed air of at least 2 Kg/cm gauge.

and up to 100 times the diameterof the yarn. If the diameter of the yarnpath exceeds times the diameter of the yarn, irregularities occur in theaction of blowing off the liquid. For practical purposes, the yarn pathhas a diameter of 0.5 to 10 mm. It is desirable that the sectional areaof the air jet pipe is not more than two times the area (generally thesectional area of the yarn path) of the nozzle to discharge air. If thearea of the jet pipe becomes large, the effect of blowing off the liquidis low as compared with an increased rate of flow of air.

The angle between the jet pipe and the yarn axis (yarn path) is between20 to C. As the air stream to be jetted out against the direction ofyarn travel becomes stronger, the efiect of removing the liquid becomeshigher. The jet nozzle for air may be merely an opening (circular ornon-circular shapes) provided in .the yarn path, or provided annularlyalong the circumference of the yarn path.

Compressed air may be heated. When compressed air is heated, the effectof drying by heat adds to the air jetting effect, but an additional stepof heating is required.

The position of fitting the nozzle may be at any place between thefrictional rotor and the wind-up device. The position between the rotorand the delivery device is convenient for a machine having the deliverydevice since the delivery device is not contaminated. For ease ofpassing the yarn, slit-like notches may be provided in the yarn path. Itis possible to swirl the air flow by providing the jet nozzleeccentrically to the axis of the yarn path, but in this case, careshould be taken not to provide the slit-like notches in a position tomake the yarn deviate from the yarn path.

The stick slipping and burning of the contact surfaces of the frictionalrotors can also be prevented by positively cooling the engagingsurfaces. The resulting yarn has some crimp irregularities (fullyallowable for limited applications), but the level of crimps and thehigh speed of processing are comparable to the abovementioned wetmethod. In addition, the scattering of the liquid can be avoided, andthe liquid does not adhere to the yarn. This method is a very goodfalsetwisting method in operability and handling from the industrialstandpoint.

The positive cooling of the yarn holding surfaces of the frictionalrotors is conveniently performed by the method shown in FIG. 5 in whichcompressed gases 1 and l are jetted out at high speed. As the gas, theuse of air is generally economical. Air is first compressed by acompressor, and if possible, cooled to the greatest possible extent, andthen jetted out from a nozzle at a place as close as possible to thesurfaces 2 and 2' of the frictional rotors. If the nozzle is of a smallopening, more than one nozzle can be provided at intervals within anallowable range on the circumferential surface of the frictional rotor,which surface does not overlap the opposing frictional rotor.Furthermore, the shapes of the jet openings of the nozzle may be madeslit-like on the circumference which does not overlap the opposingfrictional rotor. The pressure and the amount to be jetted out of airare selected according to the material of the surfaces of the rotors,the pressure of contact between the frictional rotors (to be referred-to as contact pressure), the speed of rotation, and the shape andnumber of the nozzles. Usually, the pressure of'the air is at least 0.5Kg/cm gauge, and the amount of air is at least 10 Nl/min. Compressedairmay be used after having been cooled.

In the process of the present invention, the yarn is rotated while beingheld between the engaging surfaces of two frictional rotors. In order torotate the rotors while firmly securing the yarn, the yarn holdingsurfaces of the rotors are desirably made of rubber having a hardness of40 to 70. The hardness of rubber is measurrd with a spring-type hardnesstester, in accordance with the specifications of JlS-K-630l-l962(Physical testing method of vulcanized rubber).

The surface, shape and thickness of the frictional rotors that hold theyarn affect the quality of the yarn and operability especially duringhigh speed rotation. Where the frictional rotors are rotated at highspeed, the material of the frictional rotors at the outermost peripheryis extremely deformed by a centrifugal force, and the condition ofholding the yarn changes from that at the time of holding it in astationary condition, resulting in reduced yarn holding power and yarntwisting power and accordingly an unstable operation.

In order to obtain stable holding power and twisting power at the timeof high-speed operation, it is pre ferred that the thickness of therubber with a hardness of 40 to 70 should be 0.5 mm to mm. Furthermore,the rubber should be bonded firmly to a substrate second to the rotaryshaft. It is also possible to increase the thickness of rubber beyond 5mm and provide a reinforcing outer wheel on the periphery of thesubstrate and the rubber. In the case of providing the reinforcing outerwheel, rubber is made to extend beyond the end of the outer wheel by 0.5to 5 mm. FIG. 6 shows a frictional rotor in which an outer wheel isprovided on the periphery of the substrate and rubber. In FIG. 6,annular substrate 2, and 2 are fixed to the ends of rotary shafts 1 and1 by nuts 3 and 3. To the surfaces of the annular substrates 2 and 2,rubbery elastomers 4 and 4 are attached, to thereby form frictionalrotors 5 and 5. In order to prevent the deformation of the rubberyelastomers 4 and 4 at the time of rotation in contacting relation, outerwheels 6 and 6' are secured. Preferably, the rubbery elastomers have ahardness of 40 to 70.

Yarn Y travels in the direction of the arrow, and is twisted anddetwisted. Letter D indicates the thickness of the rubbery elastomerfrom the adhering surface of the frictional rotor or from the moldsurface, and d designates the projecting thickness from the outer wheel4 to the surface of the frictional rotor material.

It has been well known that the thickness of a frictional sustance of africtional rotor from the adhering surface differs at its outermostcircumference according to the hardness of the frictional substance. Ithas been found that the upper limit of thickness D is determined by aspace above the apparatus, and with regard to the twisting, it appearsto be about 50 mm; but that the lower limit of thickness D greatlyaffects the twist ing and yarn stringing. If the thickness of thefrictional substance is less than 0.5 mm, the adhering surface of themetal exerts a great influence, and the moldulus of elasticity of thefrictional substance apparently decreases, which in turn results in areduced holding power of the yarn.

As to the projecting thickness d, it has generally been thought thatlarger thicknesses d are preferred by reason of increased number ofuses. However, it has been found that when the thickness d is increased,the projection of the outermost periphery becomes greater with highspeed rotation, and yarn breakage occurs in several hours. The limit ofthickness is therefore 5 mm.

The requirement that this thickness should be 0.5 to 5 mm will bespecifically explained with reference to an example. In this example, aZOO-denier polyethylene terephthalate yarn is processed at a yarn speedof 450 meters per minute using frictional rotors whose diameters are mm,and whose interaxial distance is 50 mm. The hardness of rubber on therotors is 60.

A. When processing was performed using the apparatus shown in thedrawings in which the thickness d from the outer wheel was 6 mm and thethickness of the rubbery substance D was 10 mm, yarn breakage occurredin 10 hours. Thereafter, the outermost circumference was deformed in theoutside direction, and it was no longer possible to string the yarn.

B. When in the processing shown in (A), the thickness d was changed to0.3 mm, fuzzes were formed frequently and yarn breakage occurred to makeit impossible to continue the processing. This is because the two rotorswere pushed with some force in the thrust direction, and the yarn heldbetween them was rubbed with the outer wheel.

C. When in the processing shown in (A), the distance d was changed to 1mm, the yarn stringing became easy, and the time required for yarnbreakage was extremely prolonged, which made it possible to producebulky crimped yarns of high quality.

D. When the processing was performed without the outer wheel whileadjusting the thickness D from the adhering surface to 0.3 mm,sufficient elastic force for holding the yarn could not be obtained, andit was impossible to string the yarn. Even if the hardness of therubbery substance is reduced, the deformation was great because of highspeed rotation, and the yarn stringing was impossible.

E. When the process was performed while adjusting the thickness D fromthe adhering surface to 10 mm and the projecting thickness d from theouter wheel to 3 mm, the twisting operation could be performed stablyand uniformly, and bulky yarns of high quality could be obtained.

The results obtained are shown in Table 9.

TABLE 9 Thick- Thickness ness Time that D d elapsed State until (mm)(mm) breakage of yarn (hours) 20 10 Large bulging of the outermostcircumference, and yarn stringing impossible 20 8 Yam breakage occurredin 5 several hours, and thereafter, yarn stringing was impossible l0 6Yarn stringing possible, but I00 stability of tension poor l0 5Processing possible, twist- 500 ing stable, high quality yarn obtained10 4 Processing possible, twist- 500 ing stable, high quality yarnobtained 10 3 Processing possible, twist- 500 ing stable, high qualityyarn obtained 10 2 Processing possible, twist- 500 ing stable, highquality yarn obtained 10 l Processing possible, twist- 500 ing stable,high quality yarn obtained 10 0.5 Processing possible, twist- S00 ingstable, high quality yarn obtained Yarn stringing possible, yarncontacted the outer wheel, considerable fuzzes Yarn stringing impossibleLarge bulging of the outermost circumference, and yarn stringingimpossible without outer wheels It is seen from Table 9 that stableprocessing becomes possible when the thickness from the mold face is atleast 0.5 mm, and the projecting thickness from the outer wheel is from0.5 to mm; and the time that has elapsed until the breakage of yarn wasgreatly increased.

In the present invention, one of the two frictional rotors may be afixed disc capable of being rotated in the circumferential direction butcompletely free of gap in the axial direction by such means as doublenuts; the other rotor is rendered rotatable both in the circumferentialand bearing directions. At this time, the movement of one disc in thebearing direction can be performed by the following mechanisms.

A. Using a radial ball bearing, the disc is made to slide between thedisc shaft and the inner lace.

B. Using a radial ball bearing, the disc is made to silde between theouter lace and the bearing housing C. The disc shaft is supported by anair bearing, and made to float completely.

With regard to (A), the following were confirmed as a result of a6-month operation.

If the clearance between the inner lace and the disc shaft, the shaftrotates between them. If a proper clearance is provided between them, notrouble occurs for practical purposes. It is however necessary to applya suitable lubricant such as grease always between the inner lace andthe shaft.

With regard to (B), troubles do not occur for practical purposes. Butdepending upon the clearance between the outer lace and the bearinghousing, the shaft does not fit straight into the bearing, and thebearing becomes heavy.

The method shown in (C) does not require lubrication, and there issubstantially no resistance with regard to the movement in the axialdirection. Thus, this is the most ideal supporting method, and there islittle deviation among the spindles.

When an air bearing is not used, solid or liquid friction occurs betweenthe shaft and the bearing, and it is necessary to increase the urgingpressure accordingly. In the case of using a multiple of spindles, thereis a difference in the variation of frictional resistance, and theresulting products differ in quality although not to an On the otherhand, the use of an air bearing render the shaft afloat by a film ofair, and therefore the frictional resitance becomes a gas friction. Theresistance is very low, and there is substantially no difference amongthe spindles. Furthermore, the life of the shaft is prolonged.

If only one of the disc shafts is rendered freely movable, the followingadvantages can be obtained.

That is, if one of the shafts is fixed, and the other is allowed to movefreely, and if the disc on the fixed shaft is swayed, the other discshaft moves and matches the swaying of the swaying disc. Therefore, theyarn can be maintained always at an equal contact pressure, and thedeviation in the quality of yarn is reduced.

But when both of the shafts are fixed,the abovementioned advantagescannot be obtained, and the swaying of the discs on both shafts are moreemphasized. Consequently, the contact pressure varies, and deviation inthe quality of yarn is caused.

The above will be explained with reference to the drawings. In FIG. 7,the reference numerals l and 2 represent discs which consist of discs ofthe same diameter rotating in mutually opposing directions. They contacteach other and deliver the yarn 3 while nipping it therebetween, andimparting twists to the yarn at the same time.

The disc 1 is secured to the disc shaft 4 and supported by radial ballbearings 5 and 6, and clamped to the disc shaft in the axial directionby double nuts 7 and 3 and thus fixed without a clearance therebetween.In FIG. 8, the reference numeral 9 is a disc shaft on the free-movingside, and supported by bearings 10 and 11. The bearings are made of analloy such as phosphorbronze, and 10 to 20 small holes 12 and 13 areprovided in a radial fashion at a place in contact with the disc shaft9. A bearing housing 14 includes channels 15 and 16 at placescorresponding to the small holes 12 and 13 provided in the bearings 10and 11. Compressed air openings 17 and 18 are connected to thesechannels through the outer circumference. Compressed air provided bypipes 19 and 20 is supplied to these holes from outside.

A radial ball bearing 21 is secured to the end of the disc shaft 9, andsupported by a bearing housing 22. A piston 23 is in contact with thebearing housing 22 through a rubber cushion at the foreward end. Acylinder 25 receives compressed air from the pipe 26, and urges thepiston 23 against the bearing housing 22. A lever 27 is integral withthe bearing housing 22, and comes in contact with the cylinder 25through a spring 28. A hole 29 is provided in the cylinder housing, andwhen the lever 27 reaches this position, the spring acts to separate thediscs from each other and fix them.

When it is desired to twist the yarn, compressed air is first suppliedfrom pipes 19 and 20 to make the disc shaft float. The lever 27 ispushed down, and air is sucked from the hole 29. In this condition,compressed air is fed from the pipe 26, whereupon the piston 23 pushesthe disc shaft 9 on the left via the ahaft housing 22, and ruges thedisc 2 against the disc 1. Since the disc shaft is completely afloat bythe compressed air, there is substantially no resistance in the axialdirection, and compressed air acting in the compressed air pipe26"directly acts on the disc 2 through the disc shaft 9.

As one example of such an apparatus, the outer diameter of-the disc wasadjusted tov mm, the diame-,.

ter of the disc shaft, 20 mm, the number of holes provided in thebearings, 10, and the air pressure on the bearing, Kg/cm Thefalse-twisting condition of a yarn was examined with the pushingpressure of the disc maintained at 3 Kg, the yarn speed at 600 meters/-min., and the speed of rotation of the disc shaft at 2,400 rpm. Thecontact pressure was hardly changed, and it was possible to conduct thetwisting operation stably.

The invention will now be described by the following Examples.

EXAMPLES l to 11 Polyethylene terephthalate yarn(PET for short) andnylon 6 yarn (N for short) were false-twisted by the false-twistingapparatus shown in FIG. 1. The frictional rotors used were made ofnitrile rubber with a hardness of 52 (Examples-l and 2), polyurethanerubber with a hardness of 55 (Examples 3, 4, 5 and 6). The thickness ofthe rubber was 6 mm. A reinforcing outer wheel was provided around thesubstrate and the rubber, and the projecting thickness of the rubberfrom the foreward end of the outer wheel was adjusted to 3 mm.

The contact pressure between the two frictional rotors was 3 kg, and theengaging surfaces between the frictional rotors were wetted with water.The length of the heater was 2 m.

The results are shown in Table l0.

using compressed air having a pressure of at least 0.5 kg/cm the liquidcontent could be reduced to less than 4 percent, and at 2 kglcm theliquid content could be reduced to 0.5 percent, and that good crimpedyams same as commercially available crimped yams could be produced.

under the conditions shown in Table 13 using frictional rotors ofnitrile rubber having a hardness of 52, and was made into stockings. Theproducts were of almost the same quality as that of the commercial gradearticle.

On the other hand, when cooling was stopped in the same proceduresviolent generation of heat between TABLE Frictional rotor Temper- YarnYarn lnter- False With- Number ature speed Yarn Twisting feed Diamaxialtwisting draw of of Example (m./ denierl speed speed eter Speed distancetension tension twists Process heater No. min.) filament ratio ratio(mm.) (r.p.m.) (mm) (gr.) F1 lgr.) F (gr.) F ability C.)

500 N 70/24 0.71 1.40 82 3.070 37 27 20 3,100 (iood. 190 500 N 100/48.73 1.37 82 3,020 35 38 2,200 (loud. 200 800 PET 75/24 .711 1.24 904,250 48 40 3,200 (iood. 220 800 PET 75/24 .81 1.23 150 2,500 83 41 233,200 (loud. 240 1.000 PET 75/24 .86 1.16 150 3,050 87 46 22 3.150(loud. 250 800 PET 150/30 .78 1.24 90 4,250 48 60 2,600 (iootl. 265

500 N 70/24 .65 1.40 82 3,300 34.6 12 12 3.350 Poor. 190 500 N 70/24 .951.30 82 2,540 48.5 66 2,300 Poor. 190 800 PET 75/24 .78 1.00 90 4.620 5570 15 2.800 Poor. 240 800 PET 75/24 .78 1.50 90 4,100 41.5 24 22 3200Poor. 240 800 PET 75/24 .60 1.45 90 4,750 36.9 Poor. 240

EXAMPLE 12 the rotors took place at a processing speed of meters A 75denier/24 filament polyethylene terephthalate yarn was processed by theapparatus shown in FIG. 1 under the conditions shown in Table l 1.

TABLE 1 1 Material of rubber nitrile rubber Outer diameter of thefrictional rotor 90 mm Inner diameter of the frictional rotor 30 mmlnteraxial distance 48 mm Hardness of rubber (.llS) 52 Contact pressure0.65 kg Length of heater 1.5 m Temperature of the heater 240 C. Numberof twists 3150 T/M Yarn feed speed Yarn withdraw speed 800 meters/min.824 meters/min.

Speed of the rotation of the frictional 4350 rpm l'OlOl' The amount ofliquid used 0.1 liters/min. Liquid water Air jet opening diameter of theliquid removing nozzle 1.5 mm

The liquid content of the yarn with the pressure of the compressed airvaried between 1 to 4 kg/cm is shown in Table 12. It is seen from thetable that by per minute. and the surface of the rubber was fused.

speed of yarn Speed of rotation of the frictional rotors Cooling method6.65 X yarn speed (m/min.) rpm gas jet method shown in FIG. 5

gas: air pressure: 3 kg/cm gauge flow rate: 200 N liter/min.

What is claimed is:

l. A process for false-twisting a yarn, which comprises passing acontinuous filament yarn through the frictional engaging surfaces of twofrictional rotors of the same diameter, said rotors facing each otherwith the rotary shafts not being on the same axis. said rotors rotatingin opposite directions toeach other and at least the'engaging surfacesof said frictional rotors are wetted with a liquid inert to the yarn,wherein said yarn is fed to said frictional engaging surfaces at a speedof at least 500 meters per minute and imparted a tension defined by thefollowing formula wherein F is the tension of the yarn in grams perdenier,

and V is the speed of feeding the yarn in meters per minute, in afalse-twisting zone, the yarn being fed to the engaging surfaces of thefrictional rotors at a feed speed which simultaneously satisfies thefollowing two conditions:

1. the ratio of the yarn feed speed to the speed component (AD) of theperipheral speed of the frictional rotors in the yarn twisting directionis from 0.7 m 0.9, and

2. the ratio of the yarn feed speed to the speed component (AC) oftheperipheral speed of the frictional rotors in the yarn deliveringdirection is from 1.05 to 1.40;

and withdrawing the yarn from the frictional engaging surfaces.

2. The process of claim 1, wherein the yarn is withdrawn from thefrictional engaging surfaces at a withdraw tension lower than thetension of the yarn in the falsetwising zone.

3. The process of claim 2, wherein the yarn is withdrawn from thefrictional engaging surfaces at a withdraw tension of not more than 80percent of the'tension of the yarn in the false-twisting zone.

4. The process of claim 1, wherein the yarn which has passed through theengaging surfaces wetted with an inert liquid and has been withdrawn inthe wet state from said engaging surfaces is subjected to the blowing ofan air stream to thereby remove the inert liquid from said yarn.

5. The process of claim 1, wherein each of said frictional rotors isconstructed of a substrate fixed to a rotary shaft, with a rubberyelastomer secured to said substrates, said rubbery elastomer having ahardness of 40 to and a thickness of 0.5 mm to 5 mm.

6. The process of claim 5, wherein each of said frictional rotors isconstructed of a substrate fixed to a rotary shaft, a rubbery elastomersecured to said substrate and having a hardness of 40 to 70, and areinforcing outer wheel provided around the substrate and the rubberyelastomer, said rubbery elastomer projecting from the forward end ofsaid outer wheel by 0.5 to 5 mm.

7. The process of claim 5, wherein one of the frictional rotors has itsrotary shaft secured to a bearing so that the bearing surface can beslided in the axial direction, and the other is supported by a bearingso that its rotary shaft does not substantially slide in the axialdirection.

8. The process of claim 1, wherein the tension imparted to the yarn isdefined by the following formula 0.70 F, 6.35 X l0V- 0.100

wherein F l and V are as defined above.

t t l l

1. A process for false-twisting a yarn, which comprises passing acontinuous filament yarn through the frictional engaging surfaces of twofrictional rotors of the same diameter, said rotors facing each otherwith the rotary shafts not being on the same axis, said rotors rotatingin opposite directions to each other and at least the engaging surfacesof said frictional rotors are wetted with a liquid inert to the yarn,wherein said yarn is fed to said frictional engaging surfaces at a speedof at least 500 meters per minute and imparted a tension defined by thefollowing formula 0.85 > F1 >6.35 X 10 4V - 0.100 wherein F1 is thetension of the yarn in grams per denier, and V is the speed of feedingthe yarn in meters per minute, in a false-twisting zone, the yarn beingfed to the engaging surfaces of the frictional rotors at a feed speedwhich simultaneously satisfies the following two conditions:
 1. theratio of the yarn feed speed to the speed component (AD) of theperipheral speed of the frictional rotors in the yarn twisting directionis from 0.7 to 0.9, and
 2. the ratio of the yarn feed speed to the speedcomponent (AC) of the peripheral speed of the frictional rotors in theyarn deliveriNg direction is from 1.05 to 1.40; and withdrawing the yarnfrom the frictional engaging surfaces.
 2. the ratio of the yarn feedspeed to the speed component (AC) of the peripheral speed of thefrictional rotors in the yarn deliveriNg direction is from 1.05 to 1.40;and withdrawing the yarn from the frictional engaging surfaces.
 2. Theprocess of claim 1, wherein the yarn is withdrawn from the frictionalengaging surfaces at a withdraw tension lower than the tension of theyarn in the falsetwising zone.
 3. The process of claim 2, wherein theyarn is withdrawn from the frictional engaging surfaces at a withdrawtension of not more than 80 percent of the tension of the yarn in thefalse-twisting zone.
 4. The process of claim 1, wherein the yarn whichhas passed through the engaging surfaces wetted with an inert liquid andhas been withdrawn in the wet state from said engaging surfaces issubjected to the blowing of an air stream to thereby remove the inertliquid from said yarn.
 5. The process of claim 1, wherein each of saidfrictional rotors is constructed of a substrate fixed to a rotary shaft,with a rubbery elastomer secured to said substrates, said rubberyelastomer having a hardness of 40* to 70* and a thickness of 0.5 mm to 5mm.
 6. The process of claim 5, wherein each of said frictional rotors isconstructed of a substrate fixed to a rotary shaft, a rubbery elastomersecured to said substrate and having a hardness of 40* to 70*, and areinforcing outer wheel provided around the substrate and the rubberyelastomer, said rubbery elastomer projecting from the forward end ofsaid outer wheel by 0.5 to 5 mm.
 7. The process of claim 5, wherein oneof the frictional rotors has its rotary shaft secured to a bearing sothat the bearing surface can be slided in the axial direction, and theother is supported by a bearing so that its rotary shaft does notsubstantially slide in the axial direction.
 8. The process of claim 1,wherein the tension imparted to the yarn is defined by the followingformula 0.70 > F1 > 6.35 X 10 4V - 0.100 wherein F1 and V are as definedabove.